Treatment of metals



Sept. 29, 1925.

G. H. HOWE TREATMENT OF METALS Filed NOV. 1923 Inventor: Goodwin H.Howe,

His Attornqg w Patented Sept. 29, 1925.

UNITED STATES PATENT OFFICE.

GOODWIN H. HOWE, O'F SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRICCOMTANY, A CORPORATION OF NEW YORK. I

TREATMENT or Marl ns.

To all whom it may aoncem:

Be it known that I, Gooowm H. Howe, a citizen of the United States,residing at Schenectady, county of Schenectady, State of New York, haveinvented certain new and useful Improvements in the Treatment of Metals,of which the following is a specification. L

My invention relates to the art of protecting metallic articles againstthe effects of oxidation suchas will ordinarily occur at hightemperatures. It is now well-known that metallic articles made ofvarious metals, such as iron and copper, may be protected againstoxidation at high temperatures by causing to be formed upon th surfaceof the article an alloy of the metal itself with another metal, such asaluminum. In a patent-isued to Tycho Van Aller, No. 1,155,974,

dated October 5, 1915, there is described and claimed a process ofprotecting metals in this way and an article of manufacture soprotected. In this patent one of the methods described consists inemploying powdered aluminum which is caused to alloy with the foundationmetal at the surface. Subsequent patents such, for instance, as patentsto Dantsizen, No. 1,381,085, dated June 7, 1921, Ruder, No. 1,346,062,dated July 6, 1920, and Ortiz, No. 1,409,017, dated March 7, 1922,describe and claim improvements upon the Van Aller patent, having fortheir objects the rendering of the treatment more effective and thesimplification of the process.

It is now well known that the aluminum or other alloying metal on thesurface gradually penetrates the article under the action of hi htemperatures. This diffusion of the alloying metal throughout thearticle in time reduces the roportion of the alloying metal at the surace, resulting in reduced protection against oxidation. I have foundthat by locating a mass of the alloying metal within the article to beprotected and then forming an alloy on the surface, high temperatureswill have the effect of causing the metal of the mass to penetrate thearticle and thus afford protection against oxidation. I have found, forinstance, that an iron or steel tube having an aluminum core between theinner and outer surfaces will withstand high temperatures for a consid-'erably longer period than would be the case with a tube treated on thesurface by the ordinary methods.

My invention is particularly well adapted for application to tubesalthough it is by no means limited thereto. I shall therefore describemy invention as applied to tubes and then point'out the scope of myinventionin the appended claims. Also, my invention is obviously notlimited to the use of aluminum as a heat protecting metal. It has broadapplication to the use of various other alloying metals, such aschromium or zirconium.

For a more complete understanding of my invention reference should behad to the accompanying drawing in which Fig. 1 is an end elevation viewof a tube constructed in, accordance with my invention; Fig. 2 is a Viewsimilar to Fig. 1 illustrating the diffusion of the alloying metal whenthe tube is subjected to high temperatures; Fig. 3 is a longitudinalsection view of a tube showing methods of sealing and closing the ends;while Fig. 4 is a longitudinal section view similar to Fig. 3 showingthe diffusion of the aluminum.

In. the accompanying drawing I have shown for purposes of illustrationone embodiment of my invention. In this case I have shown a composite orfabricated tube to which my invention is applied. This tube is made upof inner and outer tubes 10 and 11 made of oxidizable metal, such assteel or iron. Between these two tubes is an aluminum tube or core 12,the three tubes fitting tightly together and being assembled so as toconstitute in effect one tube.

As shown in Fig. 3 the ends of the inner and outer tubes 10 and ll'maybe united by making the aluminum tube 12 somewhat shorter so as to leavea space at the ends between the tubes 10 and 11 into which a ring 13 "isdriven. The ring may be made of the same material as the tubes 10 and11. A welded joint 14 is formed at the ends between the ring 13 and thetubes. A tube is thus formed which to all appearances'is a homogeneoussteel or iron tube. In some cases, for example in pyrometer tubes, itmay be desirable to close one or both ends of the composite-tube. .Thismay be done by providing a composite cap on the end to be closed. Asshown in F1g;- 3, an inner cap 15 has its rim driven in place betweenone of the methods described in the patents,

the tubes in the manner of the ring 13. Over cap 15 is placed an outercap 16 with a sheet of aluminum 17 between them. The cap 16 is suitablysecured on the end of the outer tube 11 for example by means of screwthreads 18.

The composite tube thus formed is now treated so as to cause aluminum orother suitable metal to alloy with the surface of the tube by somemethod as, for instance,

above referred to. Both the inner and outer surfaces of the tube may bethus treated 'to form thin surface layers of aluminum alloy although thetreatment need not necessarily be applied to both surfaces unlessrequired by the nature of the service to which the tube is to besubjected. One of the common uses for tubes is in oil stills, thesetubes some times being three or four inches in diameter and 20 feet ormore in length. It is usual to treat these tubeson both the inner andouter surfaces.

When the composite tub'eabove described is placed in service andsub'ected to'high temperatures the aluminum 0 the aluminum cores 12 and17 will gradually penetrate the metal of the tubes by diffusing bothinward and outward as indicated in Figs. 2 and 4. The cores provide anexcess of aluminum in the interior of the article. At the same time thealuminum of the inner and outer surface alloys 19 and 20 will graduallypenetrate and diffuse through the metal. As this diffusion of aluminumproceeds during continued use at high temperatures, the diffusionoutward from the masses of aluminum 12 and 17 will meet the diffusion ofaluminum inward from the surface alloy and have a tendency to retard orcheck the diffusion of aluminum from the surface alloy. The aluminumcontent of the surface alloy is thus maintained suiiiciently high toassure protection against oxidation when the tube is subjected to hightemperatures.

It will be observed that the diffusion of the metal of the coresforms'an internal layer of heat resisting alloy. In case of failuretherefore of the inner or outer surface layers of alloy, a completefailure of the article cannot result due to the relatively stronginternal layer of alloy. Such a failure at the surface may result fromimproper treatment during the formation of the surface layers of alloy,or it may result from subse uent mechanical injury puncturing the surace layer. The improper treatment may be due to the fact that some partsof the article are more in-accessible than others. For example, in atube having one end closed, as shown in Fig. 3, the inner surface at theclosed end may not be thoroughly treated. Complete failure of the tubehowever, will be preventedby the internal layer I of alloy. I have foundalso that the alumiand form a num of the cores 12 and 17 tends to etratethe joints between the cap 15 an the inner and outer tubes 10 and 11, asshown in Fig. 4, thus preventing failure from oxidation at these placesand also securelywelding the cap in place.

While I have described my invention as embodied in concrete-form and asoperating in a specific manner in accordance with the provisions of thepatent statutes, it should be understood that I do notlimit my inventionthereto, since various modificationsthereof will suggest themselves tothose skilled in the art without departing from the spirit of myinvention, the scope .of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. In a metallic article provided with a surface alloy with anothermetal to protect it against the effects of high temperatures, the methodof checkin diffusion of the alloying metal from to surface inward whichconsists in causing diffusion of a simi- I lar metal outward from theinterior of the article.

2. In a metallic article provided with a surface alloy with anothermetal to protect it against the effects of high temperatures, the methodof checking diffusion of the alloying metal from the surface inwardwhich consists'in providing an excess of said metal in the interior ofsaid article.

3. In a metallic article provided with a surface alloy with anothermetal to protect it against the effects of high temperatures, the methodof checkin diffusion of the alloying metal from t e surface inward whichconsists in providing a core of the alloying metal in t e interior ofthe article whereby the metal of. the core is diffused outward upon theapplication of high temperatures.-

4. The method of protecting metallic articles against the efiects ofhigh temperatures which consists in providing in the interior of thearticle a mass of a metal adapted to penetrate the metal of the articleupon the application of high temperature eat resisting alloy therewith,and then forming an alloy of said metal and the article upon the surfaceof the article.

5. The method of protecting metallic articles against the effects ofhigh temperatures which consists in inserting an aluminum core inthearticle, and then forming on the surface of'the article an alloy ofaluminum and the metal of the article.

6. The method of protecting metallic tubes against the oxidizing effectsof high temperatures which consists in first forming a composite tubehaving aluminum between the inner and outer surfaces of the tube, andthen forming on' the surface of the tube an .alloy of aluminum and themetal of the tube.

7. The method of protecting metallic tubes against the effects of hightemperatures which consists in first forming a composite tube,comprising inner and outer tubes of the metal with an aluminum tubebetween them, and then forming on the surface of the composite tube analloy of aluminum with the surface metal.

8. The method of closing a composite tube comprising inner and outertubes made of an oxidizable metal separated by a layer of an alloyingmetal adapted to penetrate the tubes upon the application ofhightemperatures and form therewith a heat resisting alloy, which consistsin securing an end member to said composite tube made of inner and outerlayers of an oxidizable metal separated by a layer of said alloyingmetal.

9. The method of closing a composite tube comprising inner and outertubes made of an oxidizable metal sepa ated by a layer of aluminum,which consists in securing a ca to said composite tube made of inner anouter layers of an oxidizable metal separated by a layer of aluminum.

10. As an article of manufacture a metallie article made of anoxidizable metal provided with an internal mass of an alloying metaladapted to penetrate the oxidizable metal upon the application of hightemperatures and form a heat resisting alloy there with, and a surfacelayer of an alloy of said alloying metal and the oxidizable metal.

11. As an article of manufacture a metallic article made of anoxidizable metal such as iron or steel having an aluminum core, thesurface metal of the article being alloyed with aluminum.

12. As an article of manufacture a composite tube having aluminumbetween the inner and outer surfaces, the surface metal of the compositetube being alloyed with aluminum.

l3..As an article of manufacture a com posite metallic tube comprisinginner and outer tubes of oxidizable metals such as iron or steel and analuminum tube between them,

.the surface metalfof the composite tube being alloyed with aluminum.

In. Witness whereof, I have hereunto set my hand this 5th day ofNovember, 1923.

GOODWIN H. HOWE.

